The proposed research will concentrate on two aspects of immunity to Trypanosoma cruzi in mice. One set of experiments will examine the role of anti-T. cruzi antibody which is cytophilic for macrophages in destruction of the parasite. These experiments will determine the development of these antibodies during the course of infection in resistant and susceptible mice, the efficacy of various antigenic preparations in inducing parasite specific cytophilic antibody, cytophilic antibody mediated enhancement of destruction of the parasite by macrophages, and the mechanism of this enhanced destruction. A second set of studies will examine immune mediated destruction of T. cruzi parasitized host cells during the course of experimental Chagas' disease. Experiments will be done to determine development of lymphocyte mediated cytotoxicity (LMC) of infected host cells in resistant and susceptible mice, the susceptibility of various host cell types to infection and immune lysis, the possibility of an autoimmune response concomitant with this immunity, the effect of immunization on development of immunity to parasitized host cells, and the presence of absence of parasite antigens on the surface of infected cells.